1. Field of the invention
The invention relates to a device and a process for feeding a dry catalyst to a liquid-filled polymerization reactor.
2. Description of Prior Art
In polymerization reaction systems, a persistent challenge is introducing catalyst to the reactor and obtaining the desired catalytic effect while minimizing undesired consequences. The problems encountered can vary by the process and catalyst used, and can arise from catalyst degradation, feeding too much or too little catalyst, plugging of feed lines, poor mixing of the catalyst with other materials, or introduction of undesired quantities of carrier materials to the process.
Gas-phase fluidized bed polymerization reactors often employ dry catalyst delivery systems such in U.S. Pat. No. 3,790,036 to Miller showing a compressed gas to deliver catalyst to the reactor. U.S. Pat. No. 3,876,602 to Calvert et al. teaches a system for continuous delivery of gas-entrained dry solid catalyst particles through capillary tubes. More recently, U.S. Pat. No. 4,774,299 to Dumain et al. discloses a device and process for moving dry catalyst powder from a storage chamber to a metering device and then to an intermediate chamber, through which an inert carrier gas is released by a fast-opening valve to sweep the powder to the reactor.
In liquid-filled reactors, however, injection of gas is usually undesirable. For example, in a slurry loop reactor the reaction mixture should not exceed the bubble point, or operability problems could result from free gas in the reactor. In such reactors, catalyst is typically prepared as a liquid or slurry and injected without a gas carrier. An example is U.S. Pat. No. 4,610,574 to Peters in which a dry catalyst and a hydrocarbon liquid are premixed to form a slurry which is sent to a solvent-filled polymerization reactor
Existing fluid streams to the reactor can also carry the catalyst U.S. Pat. No. 4,123,601 to Kellum et al. teaches an apparatus to feed controlled quantities of a hydrocarbon-slurried catalyst. A line continuously feeds an inert hydrocarbon liquid to the reactor. In this line a bypass loop is provided which is periodically charged with a predetermined amount of catalyst. At intervals the hydrocarbon liquid is fed through the bypass loop to sweep the catalyst to the polymerization reactor. U.S. Pat. No. 3,846,394 to Mitacek adds diluent at one or more point in the line to help sweep the catalyst to the reactor, thus avoiding problems arising from premature contact of catalyst with the monomer.
While suitable systems exist for delivery of slurried catalysts to liquid-filled reactors, some catalysts suffer from prolonged contact with the hydrocarbons used as solvents or diluents in the process. U.S. Pat. No. 3,012,024 to Kavesh notes this problem and teaches a process for introducing dry catalyst to a solvent-filled polymerization reactor with the object of maximizing catalyst efficiency. A compressed carrier gas such as nitrogen or ethylene conveys the catalyst to the reactor.
It is therefore an object of this invention to provide a device and process for keeping a polymerization catalyst dry before it is fed to a liquid-filled reactor. A second object is to feed precise amounts of catalyst without plugging of feed lines. Another object is to avoid introducing undesirable amounts of gas to such a reactor. A further object is to avoid problems of reactor fouling and deficiencies in catalyst activity, resin powder properties and pellet properties caused by catalyst degradation. Yet another object is to provide a device and method for contacting the dry catalyst with a modifier before it enters the reactor. Still another is to provide a means to increase reactor effectiveness by removing gas from the feed line before it enters the liquid-filled reactor. These and other objects are accomplished by the invention described below.